Problem: A group of adults and kids went to see a movie. Tickets cost $$8.50$ each for adults and $$3.00$ each for kids, and the group paid $$40.50$ in total. There were $2$ fewer adults than kids in the group. Find the number of adults and kids in the group.
Solution: Let $x$ equal the number of adults and $y$ equal the number of kids. The system of equations is then: ${8.5x+3y = 40.5}$ ${x = y-2}$ Solve for $x$ and $y$ using substitution. Since $x$ has already been solved for, substitute ${y-2}$ for $x$ in the first equation. ${8.5}{(y-2)}{+ 3y = 40.5}$ Simplify and solve for $y$ $ 8.5y-17 + 3y = 40.5 $ $ 11.5y-17 = 40.5 $ $ 11.5y = 57.5 $ $ y = \dfrac{57.5}{11.5} $ ${y = 5}$ Now that you know ${y = 5}$ , plug it back into ${x = y-2}$ to find $x$ ${x = }{(5)}{ - 2}$ ${x = 3}$ You can also plug ${y = 5}$ into ${8.5x+3y = 40.5}$ and get the same answer for $x$ ${8.5x + 3}{(5)}{= 40.5}$ ${x = 3}$ There were $3$ adults and $5$ kids.